This invention relates to chromatography, and more particularly to an improved method and cryogenic means for condensing trace air contaminates for delivery to a gas chromatograph column or the like. Even more particularly, this invention relates to improved means of the type described which is particularly suited for use in a laboratory or in the field.
As noted by Messrs. Brettell and Grob in their articles entitled Cryogenic Techniques In Gas Chromatography (Part One), in the October, 1985 issue of American Laboratory (pp. 19-32) and Part Two: Cryofocusing And Cryogenic Trapping, in the November, 1985 issue of this publication (pp. 50-66) it has long been customary in gas chromatography (GC) to utilize a cryogenic means for trapping or condensing trace contaminates out of a gaseous phase. Typically such cryogens have been liquid gases, such as liquid argon, liquid carbon dioxide or liquid nitrogen. The gas containing the contaminate is circulated through, for example a U-shaped tube containing small glass beads, or the like. The tube is immersed in the liquid cryogen, thereby causing trace contaminates to be condensed out o the gas onto the glass beads. Thereafter the tube is heated and the contaminate is revaporized and fed to the GC.
One of the principal advantages of using a liquid cryogen is its ability to lower the temperature well below ambient, for example to as low as -196.degree. C. in the case of liquid nitrogen. A primary disadvantage of liquid cryogens, however, is that they are dangerous to work with and require very cumbersome and heavily insulated handling and storage apparatus. Moreover, the liquid cryogen is consumable during use, and the sampling cycle can be very time consuming, so that liquid cryogenics have proved to be difficult and expensive to use.
In the past, a variety of cooling devices have employed heat pumps of the type based on thermoelectricity (Peltier effect). See, for example, U.S. Pat. Nos. 4,764,193, 4,744,220, 4,726,193 and U.S. Pat. No. 4,782,664. Moreover, although at least one author has suggested that such pumps could be used for cooling a GC oven, thermoelectric heat pumps have not been considered for GC sampling or trapping applications.
It is an object of this invention, therefore, to provide an improved method and apparatus of separating out and concentrating trace contaminates from gases such as air, or the like, thereby considerably simplifying cryogenic gas trapping (CGT) procedures.
A further object of this invention is to provide improved CGT apparatus of the type described which considerably reduces the size and the cost of the equipment heretofore employed for condensing trace contaminates from gaseous mixtures, or the like. Still another object of this invention is to provide improved cryogenic gas sampling apparatus of the type described which is particularly adapted for use in a laboratory surrounding, or which can be made portable to permit ready collection of contaminate samples in the field.
Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.